The invention relates to a method of operating an internal combustion engine during the engine heat-up phase depending on the engine coolant temperature, wherein the center of the combustion process is moved back to a retarded position.
In the operation of modern internal combustion engines, high efficiencies are obtained in combustion, in particular in auto-ignition internal combustion engines, so that less residual heat is present in the exhaust gas of the internal combustion engine than in internal combustion engines of lower efficiency. In modern internal combustion engines, therefore, more time passes until a cooling medium of a coolant circuit has warmed up to a temperature required for operating a heater. The generation or attainment of a specified temperature within the coolant circuit is necessary in order that sufficient heat for heating a passenger compartment can be dissipated from said coolant circuit by means of a heating heat exchanger.
Generally, local temperature peaks occur in the combustion chamber during the combustion. The coolant circuit serves to prevent a thermal overload of the materials used. The cooling medium or the coolant which is used circulates in an engine cooling system in order to dissipate the excess heat from the engine and to keep the engine at a temperature level for optimum efficiency. The coolant is conventionally composed of a mixture of a coolant concentrate and pre-treated water or drinking water. The amount of heat of an engine which is to be dissipated depends in particular on the combustion method and on the present load point. The cooling heat quantity which is to be dissipated with respect to the effective power is for example approximately one third in modern supercharged diesel engines with direct fuel injection in relation to a spark-ignition engine without supercharging. Said limited cooling heat quantity leads to a poor heating capability in particular during a warm-up phase of the internal combustion engine after a cold start at low ambient temperatures. Accordingly, heating comfort in the passenger compartment of a vehicle can only be expected in a suitable reasonably short time by means of an additional measure, for example in the form of an auxiliary heater. Compensation of the lack of heating heat can otherwise not be obtained.
In order to avoid the need for an auxiliary heater for cost, space and weight reasons, engine-internal measures are proposed for providing suitable heating comfort. The movement of the center of the combustion is a known measure with which it is possible to raise the coolant temperature by a less efficient combustion. The center position of the combustion is, on the basis of the first law of thermodynamics, that point in time during the combustion at which approximately 50% of the fuel quantity introduced into the combustion chamber has been converted. The position of the center of combustion is conventionally denoted by the associated crank angle position, that is to say a crank angle position of the piston, at which 50% of the fuel quantity involved in the combustion has been converted to heat. The center position of the combustion is likewise known as the 50% mass conversion point.
DE 101 55 339 A1 discloses a method in which an internal combustion engine is operated in such a way that, in order to reach or maintain a desired coolant temperature, a heating mode can be initiated. In such a mode, operating parameters of the internal combustion engine are set so as to meet required nominal power values for a maximum possible heat input into the coolant and/or into the exhaust gas. Here, in the heating mode, a center position of the combustion is moved in the late direction relative to a center position of the combustion in the normal mode.
Since modern engines are increasingly operated with multiple injection in order to meet future exhaust gas standards and in order to reduce the fuel consumption, it is the principal object of the present invention to provide a method for operating an internal combustion engine in which an intensified heat transfer into a coolant circuit of the internal combustion engine is obtained by means of engine operating measures.